In a conventional air braking system, air is supplied under pressure from a compressor through an air dryer and non-return valve to a reservoir, from which air is drawn via a demand valve. The air dryer typically consists of a container of desiccant, and is periodically regenerated by passing a small volume of dry air through the desiccant in reverse, and allowing this volume to exhaust to atmosphere.
Compressed air systems are widely used to operate a number of devices, and find particular use in braking systems for heavy vehicles. These systems include an air compressor which compresses ambient air and charges a storage reservoir. The compressor is engine operated and a governor or controller, responsive to the reservoir pressure, selectively enables or disables the compressor as needed. Air dryers commonly employ a drying material or desiccant through which air passes to remove moisture and limit problems associated with moisture entering brake system components. Moisture is adsorbed by the desiccant and removed from the compressed air before it is transported to the storage reservoir.
In these known systems, periodic or cyclic purging of the air dryers is required in order to purge or regenerate the desiccant. A typical air brake drying system in present day trucks functions as follows: Ambient air is drawn in through the engine air filter, which removes particulate contaminants. The air then enters the suction side of a turbocharger or super charger, which boosts the pressure to about 103 kPa (15 psig). An intercooler is used to cool the air. Most of the boosted air then enters the engine intake, but a portion of it (typically 12 SCFM, but varying according to the engine speed) flows to the air compressor. The compressor increases the pressure from about 103 kPa (15 psig) to the system pressure of about 793 to 896 kPa (115 to 130 psig). The compressed air leaving the compressor has been heated by the compression process and as a result is capable of holding a relatively large amount of water. As the air cools in the system, it loses its capability to retain as much moisture, which results in the formation of liquid water in the system. This moisture and other contaminants can be detrimental to the system in that freezing or sludge buildup can occur. Excessive moisture can also wash away needed lubricants in the valves and other air system components.
Most commercial trucks, tractors and buses use some form of air dryer to remove the unwanted moisture and contaminants from the air brake system. The most common air dryers in use today are of the desiccant variety. In a desiccant air dryer, some water condenses before it reaches the desiccant and remaining water molecules are adsorbed by the desiccant material within the air dryer. The moisture is retained by the desiccant material until a quantity of dry expanded air is flowed over the desiccant to regenerate the desiccant. If there is too long a period before regeneration occurs, then the desiccant will become saturated and the air dryer effectively stops functioning. The type of air dryer employed is a pressure swing dryer. After being dried in the pressure swing dryer, the compressed air flows to a supply tank and system reservoirs.
As is well known to those skilled in the art, the removal of moisture condensate from a compressed air system is not only vital to the efficiency of the system, but is also necessary in order to prevent such condensate from reaching any of the mechanisms or devices to which the compressed air is supplied. The presence of such condensate may cause damage or inefficient performance.